How can I make a old metal material?
@Aky-her, you write that you have "tried a bunch of tutorials"; if this one on youtube was not one you tried, it looks to me like the first four steps discussed here would be worth watching, and the fifth step on lighting if this is a display model, as opposed to use in a game. I suspect that if it is for use in a game, the lighting of an aircraft will be dependent upon the Game Engine you are making to model for use in. 

But you also write that your model is 50 meters high; that suggests to me based upon the screenshot you provide with the answer that the length is on the order of magnitude of 200 to 300 meters, and that the wingspan is 250 to 300 meters. This would require a really, really large piece of metal to make it all from the same texture!!! Other vehicles on the same order of magnitude are some of the ultra-large cargo ships, like the Malaccamax and Chinamax sizes. But these ships are not made from a single piece of metal; they are fabricated from many much smaller elements, so a repeating texture might not be such a bad thing, in this case. If it were me, I'd suggest finding a number of textures, perhaps 12 or more, and use those at random to texture smaller parts of your object. These not be 12 separate textures; rather you might use a texture that is larger than what you intend to use, and map different elements of your model to different parts of the texture. Thus gives the model an overall visual cohesion, but still reduces the appearance that you are using multiple exact copies of the same texture. 

In fact, I would suggest that using a very large texture that would be convincing, would be unconvincing in the long run, because viewers would expect to see some repetition in any very large object.